Lifting roof XPStream - making improvements

[OP827]

*New* idea:
how about cold molding technique that is used for many years in boat building, but using the thicker foam strips? Template sections would be temporarily installed along the trailer profile to form desirable shape and ~2" strips are glued side-by-side with thickened epoxy or other glue. I could even do that on top of the trailer walls, just to see the shape visually in place and avoid later fit up mistakes. That would actually create a stronger structure due to frequent rigid glue rib reinforcements inside the foam and after the roof is glassed on both sides. Should be no delamination or structural concerns there. For strips to align perfectly I could do a groove on the strip sides and insert thin plywood pieces, but It may not be really necessary .. I do not think it will be too much of work, but the result could be quite an impressive shape...

KC, Bluebunny, what do you guys think?

 

[Bluebunny-TNT]

A grand idea that is manageable and simplified. You are on to something here. The concept opens new possibilities in foam construction! Take a little time and research the technique, and lead on! Oh, and while you are being brilliant, figure a way to not make foam dust?

 

[Bluebunny-TNT]

Pondering narrow 2" thick block strips versus say 1/2" wider sheets laminated into thickness...

 

[OP827]

Bluebunny,

I figured the way to cut foam strips quick and have no foam dust flying in the shop.
It is my "hi-tech home built" dust collector made out of 25 gal plastic barrel, 5$ shop vac from kijiji superstore that I cut the bottom off, fixed it on top of the barrel and hooked it to ~15ft of 2" dust hose. I'll connect the hose to my table saw and "everything is awesome". Already did a couple full barrels of foam and wood saw dust during the build.

I may go with narrower strips say 1.5" so it is square and more flexible as I already purchased all needed foam for thebuild and it is 1.5" thick. I am not looking to change my foam stock to other thicknesses and just one layer of molding is enough complexity for me, I think.

Now I need to decide which glue to use for the roof strips glueup, thickened epoxy, Great Stuff, other, what do you think?

 

[Bluebunny-TNT]

Sorry, I do not speak foam. I'm sure others have big opinions...

Be ready to taper your widths, I believe? (Not strip savvy, either, I'm afraid)...

 

[KCStudly]

So, I had attempted to post a reply earlier but it must have been bumped.

Not sure if the stripper foamie has been done yet, but it certainly was discussed. No reason it can't work.

Don't get hung up on perfection with foam. It doesn't come in perfectly controlled thickness and no matter how you try to glue it there will be some variations. Fortunately it sands very easily (sometimes too easily! ). Shop vac works good for cleanup but does tend to clog filters quickly, so a cyclone separator is a good idea.

If you haven't already checked out GPW's FoamStream build, you should. Although his shape is Airstream like and he used thicker foam, he used very simple techniques to get compound curves and a semi-spherical nose. Worth a read. Here's the point in his build where he started layering up the front curve.

This website shows some flat patterns of complex shapes giving an idea of what I was talking about with void areas and darts in a flat pattern. Also easy to see how the flat pattern footprint will not likely be rectangular. Look at the Bucky Ball; it approaches a spherical shape like a soccer ball when formed.

I recently was messing with some sheet metal software trying to make a flat pattern for my fenders. I want the wheel opening flange to have a 3/4 inch radius onto the top, front and rear folds of flat top jeep style fenders, but I want the radius to roll along the profile, rather than butt into crisp miters. Couldn't get it to do this straight off; it wanted to clear out the whole area in the corners. Not too hard in metal to cut sections of the radius bend, hammer form them into semi-spheres, trim and weld into the corners, but it would be nice to get closer in the modeling. Maybe have to do it as a surface map using a course facet value and go from there. My point is, even with high tech software, it is easy to model the shape, but hard to translate compound curves into flat patterns.

If sanding glued foam joints you really want to use PL300 or GS, something that sets up soft like the foam board, otherwise it sands unevenly. With GG it tends to take the surrounding foam easy and leave the joint. You think you are sanding it all evenly, but then find that the joint compressed and sprang back while the surrounding area sanded off.

 

[OP827]

Thanks KC so much, I do appreciate your help and thorough response on the subject. I did read GPW's FoamStream build thread sometime ago and got inspired by the build for foam structure construction. I agree with you on glue. GG is polyurethane base glue and solid polyurethane is the thing that is resistant to abrasive wear and elastic, so GG will not work for me. GS and PL300 are good candidates, but could you please share your experience with PL300 as I got no experience with it for setting time, workability into the groove, drying time and when two surfaces are non-porous, how much time is estimated for glue to dry so I can take the roof off? If it is going to be several days, I would rather stick to GS. Let me know. Thanks KC.
Oleg

 

[OP827]

And about dust collector I built. It does have internal a fabric cone/filter (old t-shirt shaped with a piece of metal on the bottom to hold the shape) that separates the fine dust from getting the shop vac paper filter clogged. It is basically self cleaning, simple to build and works great, never need to change the fine paper filter again. Can publish some photos of the build if anyone interested.

 

[KCStudly]

I'm interested in the separator.

I've just started using the PL300. I needed something that grabbed faster for my kerfed foam on my roof and hatch.

The instructions say to just run big beads 10 inches apart and press the pieces into the beads "immediately". I chose to spread it and use a 1/8 inch V-notched trowel to get more of the sealing benefit and perhaps a tad more structural unity. I haven't done anything special for prep and it seems to have grabbed just fine; wood to foam, epoxy/weave to foam, and foam to foam. All would need to be destroyed to separate (as best that I can tell without actually destroying my work).

With the spreading method I have been using I would say that I am limited to about a 2x3 ft piece as it looks like it is starting to dry some and doesn't work as easy in that time, but remains soft and seems to grab just fine.

The texture, both wet and cured is very much like paintable window caulk, although I don't recall if it claims to be paintable and haven't tested that aspect. I have only just sanded one seam so far. It seemed manageable, but I will hold off commenting further until I have more time with it to learn the ins and outs.

Check out the last few pages of my build.

 

[OP827]

KC, thanks for sharing your experience with PL300. I'll upload pictures of the shop vac dust collector tonight once I get home.

 

[KCStudly]

 

[OP827]

Here is my home built dust collector. It is very simple, but it does the job well. White t-shirt cone pre-filter was added later to keep the paper filter clean. To keep this t-shirt pre-filter from being sucked into paper filter, there is an old pulley dropped there. The pictures should be self-explanatory. After three barrels full of saw dust and other debris from garage floor, there was no need to clean or change any filters. Basically nothing needs to be serviced, except emptying the barrel. I like it.

 

[Bluebunny-TNT]

Hi OP,
Take a look at a series of auto aero flow tunnel studies to get insight into flow characteristics? The link below to gray's garage, episode 1 is a start. Half way through episode 1 shows a "hatchback" car, with similar shape to the rear of your trailer? Note that the flow there starts at the top front of vehicle "attached". A sharp edged downslope at the front of trailer may change everything downstream. The series has helped me visualize how the air behaves...

 

[OP827]

Hi OP,
Take a look at a series of auto aero flow tunnel studies to get insight into flow characteristics? The link below to gray's garage, episode 1 is a start. Half way through episode 1 shows a "hatchback" car, with similar shape to the rear of your trailer? Note that the flow there starts at the top front of vehicle "attached". A sharp edged downslope at the front of trailer may change everything downstream. The series has helped me visualize how the air behaves...

Thanks Bluebunny. Looks like I am on a right track with my trailer overall profile. Are you saying that in order for the flow to be attached to the trailer roof, I will have to gradually raise the roof above TV height? I am not sure I understand where is a sharp edge downslope at the front of my trailer in particular if the vertical front wall will start at same or slightly lower height than TV.

 

[OP827]

My trailer profile is actually better slopped towards the back than any of those vehicles, simply because I follow the streamline with no need for backview window. And yes it is a hatchback with sharp cut of the edges in the back. In fact I plan to extend and cantliver the roof and sides a bit for better separation of the flow.

 

[Bluebunny-TNT]

Thanks Bluebunny. Looks like I am on a right track with my trailer overall profile. Are you saying that in order for the flow to be attached to the trailer roof, I will have to gradually raise the roof above TV height? I am not sure I understand where is a sharp edge downslope at the front of my trailer in particular if the vertical front wall will start at same or slightly lower height than TV.

I'm just not sure what the behavior of the airflow will be as a result of the sharp leading edge. I would expect some buffeting to occur that may intermittently stall the flow and screw up economy (but I guess). I'd suggest you go ahead and not worry too much about it, but you might consider a sturdy mounting point for a thin canard to study its effect. Pay attention to some of those armored cars that run around town. Some of them have a canard mounted above the sharp leading edge. I can make you a not-beautiful sketch of one if you need help with the concept.

 

[OP827]

Thanks Bluebunny. Looks like I am on a right track with my trailer overall profile. Are you saying that in order for the flow to be attached to the trailer roof, I will have to gradually raise the roof above TV height? I am not sure I understand where is a sharp edge downslope at the front of my trailer in particular if the vertical front wall will start at same or slightly lower height than TV.

I'm just not sure what the behavior of the airflow will be as a result of the sharp leading edge. I would expect some buffeting to occur that may intermittently stall the flow and screw up economy (but I guess). I'd suggest you go ahead and not worry too much about it, but you might consider a sturdy mounting point for a thin canard to study its effect. Pay attention to some of those armored cars that run around town. Some of them have a canard mounted above the sharp leading edge. I can make you a not-beautiful sketch of one if you need help with the concept.

If that's the point you mean, I am not concerned that it is an issue. It is located close behind TV and should not change much. In fact sharper could be better in this case. If you could sketch the canard you noted above, that would help to undderstand the idea. Thanks!

 

[Bluebunny-TNT]

I'm just not sure what the behavior of the airflow will be as a result of the sharp leading edge. I would expect some buffeting to occur that may intermittently stall the flow and screw up economy (but I guess). I'd suggest you go ahead and not worry too much about it, but you might consider a sturdy mounting point for a thin canard to study its effect. Pay attention to some of those armored cars that run around town. Some of them have a canard mounted above the sharp leading edge. I can make you a not-beautiful sketch of one if you need help with the concept.

If that's the point you mean, I am not concerned that it is an issue. It is located close behind TV and should not change much. In fact sharper could be better in this case. If you could sketch the canard you noted above, that would help to understand the idea. Thanks!

OK. I snooped through your album to get an idea of where you are going...this is a nice shot showing that the box rather close to the hitch point, with some lovely trimmed corners for maneuvering and aero.

Therefore, your box is quite close in the tow shadow; this is very good for aero. Second, your new roof line now has some upslope at the front, which I believe is helpful...In conclusion I have nothing helpful to add to what you are already doing! Great form design!

For the record I have included the canard device I was earlier referring to. Adding a canard adds drag, but sometimes can reduce drag overall if the base form causes stalling or buffeting. Your form however looks very good!

 

[OP827]

Thanks BB, appreciate that

 

[OP827]

..
Not sure if the stripper foamie has been done yet, but it certainly was discussed. No reason it can't work.
...

Once I start looking into the foam strip planking building method, I found a few links. While this method maybe new to trailer build, it is not [completely] new to a boat building:
http://www.farriermarine.com/pdf/Foamstr.pdf
http://www.westsystem.com/ss/assets/Uploads/Foam-Strip-Plank.pdf